A high-pressure system began to put its clamps on Southern Oregon today and will squeeze its tightest by Saturday, when high temperatures are expected to hit 100 degrees, according to the National Weather Service in Medford.

"It's definitely possible to see the century mark Saturday," weather service meteorologist Misty Duncan says. "It's (forecast) at 100 now, but I may have to up that a degree or two."

Wildland firefighters at the Oregon Department of Forestry also are watching the rising mercury and are ready to pull the trigger on fire-season restrictions as early as Friday, says ODF spokesman Brian Ballou in Central Point.

"That's the buzz," Ballou says. "Fire season is within touching range."

State foresters today began warning commercial timber companies and logging outfits of the coming restrictions "because we like to give people who work in the woods a few days' heads-up," Ballou says.

For the general population, the start of fire season brings with it an immediate ban on all open burning, Ballou says. However, when the season starts that likely will be the only restriction the general public will see, he says.

"But the way it's looking, we could be ratcheting the use of power equipment pretty early," Ballou says.

Ballou says there is a possibility that fire season could be held off until early next week if any rain sans lightning reaches the region, but Duncan says that 's not much of a possibility.

Holding the restrictions off until Monday or Tuesday would give rural landowners another weekend for mowing dry grass and removing brush and downed wood around their structures to make them less susceptible to burning should a wildfire move through their properties, Ballou says.

The cause behind the talk of fire season and air conditioners tripping on is a high-pressure system moving in from the Pacific that's trapping air beneath it, reducing rain and even the creation of clouds, Duncan says.

Hot spells are associated with high-pressure instances, and this one has temperatures forecast to hit 96 degrees today in Medford, then cool off a tad to 94 degrees Wednesday and 93 degrees Thursday, Duncan says.

Friday will see the temperatures ramping up again to 96 degrees, followed by 100 degrees Saturday, before dropping slowly into the high 80s early next week, she says.

Hitting the century mark for the first time the calendar year usually comes July 1, according to weather service data.

The earliest triple-digit temperatures recorded at the weather service office at the Medford airport was May 6, 1987, when the high hit 103 degrees, Duncan says. More recently, the weather service recorded 102 degrees at the airport on May 16, 2009, and 100 degrees on May 22, 2001, she says.

Ashland is forecast to be about five degrees cooler than Medford, topping out today at 91 degrees and Saturday at 95 degrees, according to the weather service.